The NIAID Division of AIDS has a requirement for the conduct of quantitative viral RNA measurements for assessment of HIV/SIV vaccine efficacy in preclinical studies with nonhuman primates. The NIAID provides immunological and virological support for nonhuman primate studies conducted at NIAID?s Simian Vaccine Evaluation Unit contract sites (SVEUs) and by AIDS vaccine researchers through three Nonhuman Primate Immunology and Virology Laboratories for AIDS Vaccine Research and Development, previously called the NHP ?Core Laboratories.? The objective of the Core Laboratories has been to ensure standardization and comparability of the assays conducted for preclinical NHP studies and to provide a common basis for assessment of the immunogenicity and efficacy of candidate HIV and SIV vaccines.